I have a 98 F-150 with a 4.6. The truck blew the #4 spark plug about 10,000 miles ago. I fixed it using a kit from napa that uses and self tapping insert and a spark plug with a longer step. Two weeks ago that insert blew out (most likely as a result of a failure of that long stemmed spark plug). I used a second kit from napa which taps and reems the head at the same time and uses and a threaded insert. Both times the inserts were put in with high temp loctite. After this second "fix" the engine began running rough. The CEL remained on and blinks intermittetly. I had the codes pulled and they read and it gave me misfire on #4 and #7. I switched the coils, replaced both plugs and both wires, drove for about 70 miles and had the codes restested. #4 and #7 still came up as a misfire. I also switched the injectors between #4 and #1 which had no effect. Any one have any ideas?


Sorry for the long post but I wanted to put the whole story down.

 

When the SES starts to "FLASH" the ECM is telling you the engine has exceded 1.5 times the FTP(Federal Tail Pipe) emissions standards. You're a big polluter at this point according to the EPA. Cy#4 and #7 are on different banks so they don't have a lot in common you can rule out. Backtrack over your steps. Did you do anything on bank 2 that would now cause #7 to start acting up when your original problem was only #4.

 

i had this recently done on my 02 5.4. Would have originally cost under 200 bucks to fix. took it to a guy since i was at school (otherwise i would do it myself). he ended up hitting the valve with the tap which a little nick won't hurt it but it turned the valve and put several in it and bent the valve. could be the problem, which luckily the guy paid half the bill and i only had to pay 550 to pull the head, new gaskets, and fix the valve.

how this relates to you, i heard, and in a recent post someone said that a misfire in one cylinder could trick the computer into saying that it is a misfire in another cylinder. also, could shavings be in the cylinders?

I had this same problem, best of luck.

 

How did you find out that you had hit the valve? Did you do a compression test to find it?

 

I have seen those kits. If it is the one I think it is ,they work like self tapping oil pan plug repair kits. The self tapping insert goes in with loctite and is meant to be left in permanently then the newer style slim spark plugs are to be used from then on . There is no way you could have tagged a valve the insert does not go that deep.
When you said that you blew another plug did the insert come out or did the plug come out of the insert ?